Method of and apparatus for measuring and controlling the rate of carburization of a melt

ABSTRACT

The carburization of a steel melt is controlled during the refining of the melt while a refining flame appears on the melt surface. The flame is spectrometrically monitored and wavelengths other than those characteristic of carbon monoxide and carbon dioxide are filtered from the spectrum. The intensities of the wavelengths characteristic of carbon monoxide and carbon dioxide are measured and a parameter of the refining is controlled in response to the combined intensities. A single relatively broad band of the flame spectrum can be monitored, this band encompassing the wavelengths characteristic of carbon monoxide and carbon dioxide, and reference values can also be measured so as to allow mathematical elimination of error resulting from smoke or like variable obscuring action.

Baumert Sept. 2, 1975 METHOD OF AND APPARATUS FOR MEASURING AND CONTROLLING THE RATE OF CARBURIZATION OF A NIELT Inventor: Jean Baumert, Esch-sur-Alzette,

Luxemburg ARBED Acieries Reunies de Burbach-Eich-Dudelange S.A., Luxembourg, Luxemburg Filed: Feb. 11, 1974 Appl. No.: 441,508

Assignee:

Foreign Application Priority Data Feb. 12, I973 Luxemburg 67003 References Cited UNITED STATES PATENTS S PE CTWK 3,831,030 8/1974 Wrobel et a]. 250/339 Primary Examiner-Archie R. Borchelt Attorney, Agent, or Firml(arl F. Ross; Herbert Dubno 5 7] ABSTRACT The carburization of a steel melt is controlled during the refining of the melt while a refining flame appears on the melt surface. The flame is spectrometrically monitored and wavelengths other than those characteristic of carbon monoxide and carbon dioxide are filtered from the spectrum. The intensities of the wavelengths characteristic of carbon monoxide and carbon dioxide are measured and a parameter of the refining is controlled in response to the combined intensities. A single relatively broad band of the flame spectrum can be monitored, this band encompassing the wavelengths characteristic of carbon monoxide and carbon dioxide, and reference values can also be measured so as to allow mathematical elimination of error resulting from smoke or like variable obscuring action.

8 Claims, 3 Drawing Figures PATENTEDSEP 21915 3,903,014

SHEET 2 0f 2 ELE III 30 COMPUTER spzcmombrs METHOD OF AND APPARATUS FOR MEASURING AND CONTROLLING THE RATE OF CARBURIZATION OF A MELT FIELD OF THE INVENTION The present invention relates to a method of and an apparatus for inspecting and controlling the decarburization of a steel melt. More particularly this invention concerns the smelting of steel in an LD, LDAC, or similar type of converter.

BACKGROUND OF THE INVENTION In the smelting of steel using the basic oxygen process it is necessary to monitor the chemical transformations in the melt relatively closely, so that the process can be stopped when the melt has obtained the desired composition. Since the process is carried out at high temperatures, well in excess of lOOOC, with the generation of a great deal of hot gasses, smoke, and the like tending to obscure the operation, it is difficult to keep track of the composition and refining stage of the melt.

The most common method of monitoring the refining operation is to continuously analyze the gases which are generated by the smelting operation, these gases comprising mainly carbon monoxide (CO) and carbon dioxide (CO the former being formed by the oxidation of the carbon in the melt and the latter being formed by the partial combustion of the so-formed carbon monoxide.

It is thus possible to measure the decarburization rate or degree by measuring the percentage of carbon monoxide and carbon dioxide in the stack gases. The principal disadvantage of this method is however that there is a substantial time lag between the instant at which the analysis of the stack gases is made and the time when these gases were generated by' the melt. Frequently it is too late to carry out necessary corrective operations. I

Another method uses the intensity of infrared light generated by the flames on the surface of the metal. Such an arrangement is substantially faster than the gas analysis which also requires relatively expensive analysis equipment. These flames on the top of the melt have a light intensity which can be related mathematically to the extent of decarburization of the melt. Clearly such a method is relatively rapid. Nonetheless is has the principal disadvantage that some melts generate relatively opaque gases which tend to obscure the flame and therefore give false readings. Also even within a normal run it is possible for the flame of one melt to be much more intense than the flame of another melt of relatively equivalent composition. Thus the results are often inaccurate.

OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide an improved method of measuring the extent of carburization of a melt.

Another object of this invention is to provide a method of and an apparatus for controlling decarburization of a melt.

A further object is the provision of a method of and an apparatus for monitoring and controlling the decarburization in a melt, which is relatively fast acting, and which gives accurate readings of the extent of carburization of the melt.

SUMMARY OF THE INVENTION These objects are attained according to the present invention with a system wherein the intensity of the infrared radiations of the flame on the melt is detected at the frequencies corresponding to those characteristic of carbon monoxide and carbon dioxide, by suppressing with filters the undesirable wavelengths. This is done with photoelectric cells producing electrical signals which constitute an output directly related to the extent of decarburization in the melt, and readily usable to vary any parameters of this melting process.

According to other features of this invention the frequencies corresponding to the infrared radiation given off by carbon monoxide and carbon dioxide, which are relatively close together, are picked up by a single broad-band detector. Alternately it is possible to use a pair of extremely narrow-band photocells of the germanium or silicon type each for one of the gases. Thus according to the present invention the response timeis almost immediate. The intensity of infrared radiation of the flame at the top of the melt forms a defined mathematical relationship to the percentage of carbon remaining in the melt and therefore can be used to calculate the extent of decarburization of this melt.

It is also possible to employ thermal sensitive elements which generate an electrical output proportional to the amount of heat detected, since infrared radiation is detectable as heat.

Thus according to the present invention infrared radiation having a wavelength of 2.3 microns is detected for carbon monoxide and infrared radiation having a wavelength of 2.7 microns is detected for carbon dioxide. It is of course within the scope of the present invention to sense a relatively broad range, stretching between 2 microns and 3 microns, to include both these compounds. In a case of melt generating a great deal of water vapor, it is possible to use a secondary band having a length of 4.3 microns for the CO which would otherwise be mainly obscured by the water vapor.

The signals derived from sensing the intensity of specific bands for the specific gases vary as a function of the temperature of the flame, which is not always in a direct proportion with the instantaneous concentrations of carbon dioxide and carbon monoxide rising from the melt. According to the present invention this deviation is eliminated or at least neutralized by providing in each measuring circuit a second filter-detector assembly which is sensitive to a different wavelength near to that part of the band of the spectrum chosen for the particular gas measuring. Since both of the intensities will vary with the temperature of the melt, it is possible to use this latter set point or reference value to cancel out the variations in the detected value of the wavelength corresponding to the composition being monitored. Thus the signal output, for instance, indicating the intensity of carbon-monoxide infrared radiation is divided by the signal output of infrared radiation having a frequency relatively close to that of the carbon monoxide infrared radiation. This method eliminates the effects of water vapor, temperature, or smoke on the radiation emitted by the flame on the melt.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become more readily apparent from the following, reference being made to the accompanying drawing in which:

FIGS. 1 and 2 are schematic diagrams illustrating the method according to the present invention; and

FIG. 3 is a largely diagrammatic view illustrating a control system according to this invention.

SPECIFIC DESCRIPTION The control circuit shown in FIG. 1 comprises four cut-on infrared filters 10, I5, 20, and 25 each arranged next to a respective infrared cut-off filter l, and The filters l0 and 10' allow infrared light having a wavelength of 2.3 microns to pass and the filters 20 and 20' allow infrared light of a wavelength of 2.7 microns to pass, corresponding to AA, and AA respectively. The filters l5 and 15 allowa wavelength AM to pass which is slightly above 2.3 microns and the filters 25 and 25 allow a wavelength AM slightly above 2.7 microns to pass. These filters are of the interference type, although it is equally within the scope of this invention to use absorbing filters.

The light passing through these sets of filters then falls on respective photocells ll, 16, 21, and 26 where it is transformed into signals indicated at U U U and U The signal U is divided by the signal U in a divider I2 and the signal U is divided by signal U and another divider 22. The quotients of these operations are combined in an adder 13. Since the light as frequencies Altand AA, will vary according to smoke conditions and temperature much as the light at 2.3 microns and 2.7 microns corresponding to that infrared radiation emitted by hot carbon monoxide and carbon dioxide, the quotients will be independent of any interference caused by such smoke, vapor, or the like. Another divider 14 serves to calculate the latest change of the two quotients added together in adder 13, so as to give a reading proportional to the decarburization rate.

The arrangement shown in FIG. 2 is similar to that of FIG. 1 except that a relatively broad-band filter 27 is used formed of a first infrared filter 28 which only allows infrared radiation having a wavelenth greater than 2 microns to pass and a filter 28 only allowing infrared radiation having a wavelength less than 3 microns to pass. Light at a wavelength of AM, is thus passed through this pair 27 of filters and is received by a photocell 29 which generates an output U which is fed into a calculator 30 into which various other outputs, corresponding to such variables as the input rate of oxygen and the like. The output of this computer is fed as shown in FIG. 3 into a motor 32'which raises and lowers an oxygen lance 33 whose output of oxygen is con trolled by a valve 34 also connected to the computer 30. The oxygen issuing from the lamp 33 is directed at this melt in a crucible 34 and a spectroscope 35 examines the flames arising therefrom. This spectroscope 35 is provided with the filters described above. The output of oxygen from the lance determines not only the decarburization rate, but also determines the shape of the jet directed at the melt, and the rate at which melt heats I claim:

1. A method of controlling the decarburization of a steel melt during the refining thereof while a refining flame appears over the surface of the melt, said method comprising the steps of:

training a spectrometric detector directly on the melt;

spectrometrically monitoring said flame from said steel melt with said detector and filtering from the infrared spectrum generated by flame wavelengths other than those characteristic of carbon monoxide and carbon dioxide;

measuring the intensities of the infrared radiation of the wavelengths characteristic of carbon monoxide and carbon dioxide; and

controlling a parameter of the refining of the melt in response to the measured intensities.

2. The method defined in claim 1 wherein wavelengths are filtered from said spectrum which lie without a band including the wavelengths characteristic of carbon monoxide and carbon dioxide.

3. The method defined in claim 2 wherein said band includes wavelengths between 2 microns and 3 microns.

4. The method defined in claim 1 wherein wavelengths are filtered from said spectrum which are different from the wavelengths of 2.3 microns, corresponding to carbon monoxide, and 2.7 microns, corresponding to carbon dioxide.

5. The method defined in claim 1, further comprising the step of measuring the intensity of at least one further wavelength of said spectrum different from the wavelengths characteristic of carbon monoxide and carbon dioxide and comparing the intensity at this further wavelength with the intensities of said wavelengths of carbon-monoxide and carbon dioxide to eliminate the effect of temperature, smoke, and the like on said spectrum.

6. An apparatus for controlling the decarburization of a steel melt during the refining thereof while a refining flame emitting infra-red rays appears on the surface of the melt, said apparatus comprising:

means trained on the steel melt for monitoring the infrared spectrum of said flame and including means for filtering from said spectrum wavelengths other than those characteristic of carbon monoxide and carbon dioxide;

means connected to said means for monitoring for measuring the intensities of the wavelengths characteristic of carbon monoxide and carbon dioxide and for generating an output representing said intensities; and

means connected to said means for measuring receiving said output for controlling a parameter of the refining of said melt in response to said output.

7. The apparatus defined in claim 6 wherein said filter means includes a CO filter passing infrared radiation of a wavelength of 2.3 microns and a C0 filter passing infrared radiation of a wavelength of 2.7 microns.

8. The apparatus defined in claim 6, further comprising means for monitoring said infrared spectrum and filtering therefrom wavelengths near those characteris tic of carbon monoxide and carbon dioxide and generating an output representing the intensities of the infrared radiation at the neighboring wavelengths, and means for comparing each of the intensities characteristic of carbon monoxide and of carbon dioxide with a respective one of the intensities of said neighboring wavelengths. 

1. A METHOD OF CONTROLLING THE DECABURIZATION OF A STEEL MELT DURING THE REFINING THEREOF WHILE A REFINING FLAME APPEARS OVER THE SURFACE OF THE MELT, SAID METHOD COMPRISING THE STEPS OF TRAINING A SPECTROMETRIC DETECTOR DIRECTLY ON THE MELT, SPECTROMETRICALLY MONITORING SAID FLAME FROM SAID STEEL MELT WITH SAID DETECTOR AND FILTERING FROM THE INFRARED SPECTRUM GENERATED BY FLAME WAVELENGTHS OTHER THAN THOSE CHARACTERISTIC OF CARBON MONOXIDE AND CARBON DIOXIDE, MEASURING THE INTENSITIES OF THE INFRARED RADIATION OF THE WAVELENGTHS CHARACTERISTIC OF CARBON MONOXIDE AND CARBON DIOXIDE, AND CONTROLLING A PARAMETER OF THE REFINING OF THE MELT IN RESPONSE TO THE MEASURED INTENSITIES.
 2. The method defined in claim 1 wherein wavelengths are filtered from said spectrum which lie without a band including the wavelengths characteristic of carboN monoxide and carbon dioxide.
 3. The method defined in claim 2 wherein said band includes wavelengths between 2 microns and 3 microns.
 4. The method defined in claim 1 wherein wavelengths are filtered from said spectrum which are different from the wavelengths of 2.3 microns, corresponding to carbon monoxide, and 2.7 microns, corresponding to carbon dioxide.
 5. The method defined in claim 1, further comprising the step of measuring the intensity of at least one further wavelength of said spectrum different from the wavelengths characteristic of carbon monoxide and carbon dioxide and comparing the intensity at this further wavelength with the intensities of said wavelengths of carbon-monoxide and carbon dioxide to eliminate the effect of temperature, smoke, and the like on said spectrum.
 6. An apparatus for controlling the decarburization of a steel melt during the refining thereof while a refining flame emitting infra-red rays appears on the surface of the melt, said apparatus comprising: means trained on the steel melt for monitoring the infrared spectrum of said flame and including means for filtering from said spectrum wavelengths other than those characteristic of carbon monoxide and carbon dioxide; means connected to said means for monitoring for measuring the intensities of the wavelengths characteristic of carbon monoxide and carbon dioxide and for generating an output representing said intensities; and means connected to said means for measuring receiving said output for controlling a parameter of the refining of said melt in response to said output.
 7. The apparatus defined in claim 6 wherein said filter means includes a CO filter passing infrared radiation of a wavelength of 2.3 microns and a CO2 filter passing infrared radiation of a wavelength of 2.7 microns.
 8. The apparatus defined in claim 6, further comprising means for monitoring said infrared spectrum and filtering therefrom wavelengths near those characteristic of carbon monoxide and carbon dioxide and generating an output representing the intensities of the infrared radiation at the neighboring wavelengths, and means for comparing each of the intensities characteristic of carbon monoxide and of carbon dioxide with a respective one of the intensities of said neighboring wavelengths. 